1. Field of the Invention
The present invention relates to a three-dimensional image capturing device that obtains three-dimensional information of a measurement subject, based on luminous information obtained by photographing the subject.
2. Description of the Related Art
In these past few years, three-dimensional image technology has been developed, and a three-dimensional image capturing device, which can sense distance information of a subject, has been put into practical use. There are various ways of sensing three-dimensional information of a subject. In particular, there is known a system combining a camera, having a high-speed shutter function, and a modulation unit, for varying the intensity of the distance measuring light beam in accordance with time. In this system, the distance measuring light beam, of which the intensity is modulated, is irradiated onto a subject, and the delay of the reflected light beam, generated in accordance with the distance between the light source and the surface of the subject, is sensed by the high-speed shutter camera, so that the three-dimensional shape of the subject is obtained.
Regarding the light source, it is preferable to use an LED in which the intensity of light is adjusted by changing the electric current, and a plurality of LEDs are electrically connected in series so as to simultaneously adjust therein, intensities. However, since the intensity of light of an LED depends upon the ambient temperature, it is necessary to feedback-control the change in the intensity of light while monitoring it. This creates a particular problem in that the control circuit for controlling the change of intensity of light over a wide range for a single LED is complicated and bulky.
Therefore, an object of the present invention is to provide a three-dimensional image capturing device in which the amount of light supplied to the light source irradiating the distance measuring light beam is stably controlled with a simple circuit.
According to the present invention, there is provided a three-dimensional image capturing device, comprising a light source, a modulating processor, a light sensing processor, and a distance obtaining processor.
The light source has a plurality of irradiating units to irradiate a distance measuring light beam to a subject. The intensities of the distance measuring light beams are different from each other. The modulating processor selects at least one of the irradiating units and modulates the intensity of the distance measuring light beam in accordance with the time elapsed from when the light source started irradiating the distance measuring light beam. The light sensing processor senses the distance measuring light beam reflected by the subject in accordance with a timing of the modulation, to obtain luminous information of the subject. The distance obtaining processor obtains distance information of the subject based on the luminous information.
The irradiating unit preferably has a plurality of LEDs that are annularly disposed along an outer periphery of a lens barrel in which a photographing lens is provided, and the LEDs are electrically connected to each other in series. In this case, the modulating processor simultaneously controls electric current flowing in each of the LEDs. Due to this, the modulation of the intensity of distance measuring light beam can be stably performed with a simple circuit.
The plurality of irradiating units maybe concentrically disposed to each other, and may have first, second, third, fourth, and fifth irradiating units, which are arranged from the center to the outmost periphery in this order. The ratio of the intensities of the distance measuring light beams of the first, second, third, fourth, and fifth irradiating units may be 1:2:4:8:16. If this ratio is used, the distance measuring light beam can be uniformly irradiated, and the intensity can be easily modulated stepwise, i.e., in 32 steps by selecting the combination of irradiating units which are to be turned ON.
Preferably, the luminous information comprises first and second luminous information, the first luminous information being obtained by increasing the intensity stepwise using the modulating processor, the second luminous information being obtained by decreasing the intensity stepwise using the modulating processor. The distance obtaining processor can obtain the distance information using the first and second luminous information. Therefore, highly accurate distance information is obtained that does not depend on the reflectance on the surface of the subject nor the uneveness of the distance measuring light beam in space.